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Acoustics — intelligent solutions for more efficiency, comfort and dynamics.

Wed May 19 16:30:00 CEST 2010 Press Release

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New, intelligent measures in acoustic lightweight construction not only insulate against undesirable noises in the passenger compartment in an especially efficient manner, but also reduce weight and thus contribute to the total efficiency of the vehicle. But, at BMW, a high degree of comfort is not everything – not by a long shot. A current research project at the BMW Research and Innovation Centre focuses on the actively designing engine sounds in the passenger compartment, making driving dynamics even more tangible — the so-called Active Sound Design.

In order to be able to drive comfortably and efficiently at the
same time, the developers look for solutions in acoustic lightweight
construction with acoustically effective components for increasing
comfort and also yielding benefits in weight and installation space
through intelligent material concepts. In this way, the customer
gains a functional advantage with lower weight and more pleasure for
lower fuel consumption and CO2 emissions. The minimisation of
background noises normally requires the use of heavy insulating and
dampening materials. This minimises surface vibrations. Nowadays
engine parts are becoming lighter and lighter through new materials,
while efficiency requirements rise, which means that crankcases, for
example, are being made out of aluminium and there is a lack of
material insulating against disturbing combustion noises.
Intelligent measures are in demand for maintaining driving comfort.
Acoustic engineers achieve this through systematic reinforcement of
the crankcase, among other things. The procedure known as
"ribbing" systematically minimises disturbing emanations
and the crankcase remains, all in all, very lightweight. In
addition, the engine is partially encompassed by an acoustic
capsule. These absorber or insulation components require little
installation space, are lightweight and at the same time quite
effectively reduce noise emanation. Absorption and insulation
directly at the engine has additional benefits to efficiency: if
disturbances are reduced directly at the source, no costly,
difficult insulation of the passenger compartment is necessary. This
helps reduce material, weight, and fuel consumption.

Another method of acoustic lightweight construction for
increasing comfort and efficiency is the integration of acoustic
functions in the existing vehicle parts. In the undercarriage
structure in use with current BMW models, which improves
aerodynamics, a LWRT (lightweight reinforced thermoplast) replaces
the former subframe made of polypropylene, which was heavier and
fitted with more absorption material, and took up more space. With
the new undercarriage structure, the absorption function is already
integrated into the surface of the subframe. This reduces weight and
installation space, while considerably enlarging the absorption
surface at the same time. Only two to eight millimetres thick, as
opposed to the previous maximum of 30 millimetres, the new structure
is significantly thinner than before and only half as heavy as the
previous structure of subframe plus additional shock absorber.

While the acoustic lightweight construction helps to fine-tune
vehicle acoustics and increase comfort, active systems, such as
Active Sound Design, ensure that the engine produces a dynamic sound
during acceleration, because vehicle dynamics are an auditory
phenomenon. With Active Sound Design, engineers can create the sound
that best fits the vehicle character or even fulfil drivers'
individual auditory desires.

"To create the desired acoustic patterns, we're refining
the natural character of the engine with an electro-acoustic system
so that acceleration becomes a special audio experience and provides
even more pleasure."

Presented in a MINI prototype for petrol engines in 2009, Active
Sound Design now also helps diesel engines achieve a sporty sound
that wasn't possible for this type of engine until now. The sporty
performance characteristics of modern diesel engines and their high
torque, especially when starting up and accelerating, contradict the
acoustic sensation of diesel vehicles. Harsh ignition impulses
during combustion, which are inherent to diesel engines' function,
are responsible for their characteristic noises — commonly
referred to as "knocking". This undesirable acoustic
characteristic of diesel engines has been brought to a very low
level at the BMW Group through intelligent acoustic lightweight
construction. This makes room for Active Sound Design, which
supports a sporty sound quality. It makes outstanding driving
performance audible.

In order to have a special audio experience and for a diesel
vehicle to sound really sporty, sound designers have to optimally
adjust the sound to the vehicle and its engine performance. Too much
sound with too little engine power would make a negative impression.
The engine sound must constantly provide for a harmonious driving
experience. The particular challenge is allocating the right dosage
of sound in all driving situations and creating an authentic audio
character. An active system allows for significantly more systematic
and finer adjustments than classic sound design, which is oriented
on the intake or exhaust system.

"Even small changes to vehicle sound can have a big impact,
since human hearing subconsciously evaluates acoustic surroundings
like a high-performance analyser and all changes are continuously
registered in the brain."

(Dr. Alfred Zeitler, Acoustic Psychologist)

The test vehicle, a BMW 635d, is sound-optimised by means of
sound design and has its own very dynamic audio character. The noise
typical for diesel vehicles disappears and instead, the driver hears
a sporty, superior sound. The entire rpm range is accompanied by
harmonious, varied and consistently appealing acoustics that make
the enormous torque audible at lower rpms and also provide for fun
at high rpms. Through Active Sound Design, diesel engines finally
achieve the engine sound that their performance deserves.

Acoustic lightweight construction — the added value is
in the interplay.One of the main tasks of vehicle acoustics in the premium
segment is to eliminate undesirable noises and to fine-tune the
sound in order to be able to shape it fittingly to the vehicle.
Nothing must buzz, groan, squeak, whistle or rattle, and disturb the
driver. The measure necessary to achieve this normally increased
vehicle weight and thus increased fuel consumption and elevated CO2
emissions. BMW is taking another route with intelligent measures in
acoustic lightweight construction. New, integrated solutions that
unite several functions not only insulate against undesirable
background noises in the passenger compartment, but reduce weight at
the same time, contributing to the vehicle's overall efficiency.

In order to be able to drive comfortably and efficiently at the
same time, the developers research possibilities to improve the
acoustic functions of different parts in acoustic lightweight
construction and to yield concepts for additional benefits to both
weight and installation space through intelligent functional
integration. For this reason, engineers are first trying to take
full advantage of available system solutions with respect to
acoustics. An absolute basic requirement for this is an integral
understanding of the vehicle's acoustic interrelationships.

"The in-vehicle acoustic causal loop is highly complex.
However, once you understand it, numerous possibilities for
optimisation reveal themselves — in terms of optimal and
efficient vehicle design."

(Tomasz Jedraszek, Manager of Airborne Sound Team)

The objective of the engineers is to combine components that are
as lightweight as possible with the optimal fulfilment of various
and often conflicting requirements for parts related to driving
operation. For acoustics, this specifically means that the correct
insulation and absorption materials must be effectively put to
optimum use for their purpose, because not all insulating material
is the same. Different materials have different properties, which
means that they're not all suitable for every purpose.

Intelligent use of materials — in the end it's the total
weight that counts.The first step to an acoustically-optimised vehicle is the
minimisation of background noises. This is normally accomplished
through the use of insulating and dampening material against
bothersome vibrations. A heavy part doesn't vibrate as much as a
light one and thus emits or transfers less sound. But the old
acoustic rule "mass is only replaced by more mass" is
outdated thanks to intelligent acoustic lightweight construction.
Systematic acoustic measures that act at the source, intelligent
sound insulation concepts, and the use of highly absorbent materials
in vehicle construction refute this old rule. These intelligent
measures permit tangible increases in comfort without significant
additional costs. The customer benefits from better acoustics at a
lower weight — more pleasure with lower fuel consumption and
CO2 emissions.

"We're not creating a light structure at any cost. It's
more about intelligent use of materials with a simultaneous increase
in efficiency, dynamics and comfort."

(Tomasz Jedraszek)

In body construction, extremely hard steels are used in places
where high rigidity standards must be met. For larger parts, lighter
materials are used, such as aluminium. Attention is paid
toensure that the right material is always
used in the right place, depending on intended use. If, for example,
only aluminium was used, it would be necessary to apply additional
material to places that are exposed to more noise to attain the
desired dampening result. This would cause the weight advantage over
steel to be lost. This method would even entail considerable
disadvantages with regard to costs and installation space.

Ribbing against background noises.In order to attain the lightest structure possible, the drive
engineers strive to systematically employ light materials. That's
why crankcases are now being made of aluminium instead of grey cast
iron. This material reduction, however, also means that the
crankcase walls are thinner, which increases the emanation of sound.
Acoustic engineers counteract this through systematic reinforcement
of the crankcase — so-called ribbing. Long reinforced bars run
along the entire crankcase. These rigidity measures serve to
systematically stabilise the surface and thus reduce bothersome
emanations, without negating the benefit to weight. Intelligent use
of materials combines the benefits of weight reduction with acoustic
insulation and dampening of a structurally-reinforced crankcase.

Noise dampening directly at the source.Engineers are constantly searching for new possibilities for
optimisation, with the goal of achieving a solution that is as
integrated as possible. They apply the principle of working as
closely to the source as possible. For instance, instead of
increasing noise-dampening at the wall between the engine and
passenger compartments, the engine is fitted with efficient
absorption materials. These materials are easy to apply and minimise
emanation of bothersome noises quite effectively. This is
advantageous not only for vehicle occupants, but also the
environment. This technology is likewise applied in other places.
Absorption materials ensure that minimal noise emanates from the
wheel housing into the passenger compartment and vehicle
surroundings. The more sound that is absorbed at the source, the
less it must be dampened on the way to the interior. This helps
reduce materials and weight, and decreases fuel consumption.
Furthermore, the dampening can have extremely positive effects on
other aspects, such as the storage of residual engine heat for the
next engine start.

Acoustic functional integration makes something that's good
even better.Another method of acoustic lightweight construction for
increasing comfort and efficiency is the integration of acoustic
functions in existing vehicle parts. This might entail, for example,
reworking the entire undercarriage and developing a compelling
solution for functionality and acoustics. Here, the fields of
aerodynamics and acoustics unite their knowledge. Until now, a
relatively heavy polypropylene subframe was used. For diesel
engines, it was also fitted with a large noise-dampening absorption
pad. With the new undercarriage structure, which is used in all BMW
models, the absorption function is already integrated into the
subframe, which reduces weight and required installation space. The
new LWRT subframe (lightweight reinforced thermoplast) has an
open-pored surface with an absorbent core. Only two to eight
millimetres thick, as opposed to the previous maximum of 30
millimetres, the new structure is significantly thinner than before
and only half as heavy as the previous one, which was composed of
the subframe and additional shock absorber. The entire surface of
the undercarriage is used, whereby the absorption surface is overall
significantly larger and the increase in comfort is greater. In
addition, the material is flexible and can be pressed down to two
millimetres at the connecting points to the body. This allows all
functions (aerodynamics, undercarriage protection and acoustics) to
be optimally integrated and at the same time space and weight is reduced.

Noise-dampening is mandatory — sound design is freestyle.But at the BMW Group, a high degree of comfort is far from
everything. A current research project of the BMW Group's acoustic
engineers concerns not only the acoustic fine-tuning of the vehicle,
but also enhancing the driving experience through Active Sound
Design.

Diesel engines present a special acoustic challenge with regard
to background noises and audible dynamics. The combustion process in
a diesel engine is not as homogeneous as in a petrol engine. The
ignition sequences in the combustion chamber are more intense and
louder. This is transferred to the adjacent parts and emanates into
the surroundings and causes the "knocking" sound that is
typical of diesel engines and inherent in their design. Due to the
harsher firing pulses, a diesel engine is considered more unpleasant
to the ear than a petrol engine.

In order to compensate for these acoustic disadvantages,
dampening could be increased. However, use of heavy materials on the
engine housing negates the benefits to efficiency of the lightweight
aluminium engine block. Acoustic engineers demonstrate how to make
an efficient diesel engine still sound comfortable and even dynamic
through acoustic lightweight construction in combination with Active
Sound Design.

Design the sound experience with active sound design.Although the acoustic lightweight construction helps increase
vehicle comfort and efficiency, engineers at BMW always carefully
ensure a special driving experience as well. After all, the brand
name stands for "driving pleasure". Since insulation makes
the engine's operation less perceptible, this first of all means a
"loss in sound" and a drop in discernible driving
dynamics. As tests show, besides physically measurable longitudinal
and lateral acceleration, the sound of acceleration also makes a
decisive contribution to the sensation of driving dynamics.

With the use of active systems for sound design, engineers can
actively shape and optimise interior sound and thus systematically
influence "heard" dynamics. In order to produce the
desired sound patterns, the natural sound of the engine is
intelligently refined with an electro-acoustic system. A digital
signal processor interactively generates additional sound components
based on constantly updated driving data so that a harmonious
overall impression is formed. Initial research projects have already
shown how effective that is. In a MINI prototype presented in 2009,
a four-cylinder engine can be made to sound like a powerful V8
engine or superior straight-six engine. Besides the fun factor
presented by individualisation, Active Sound Design also has very
serious applications, such as helping diesel engines attain even
sportier sound characteristics.

An experiment demonstrated what potential this has. The BMW
engineers took two identical vehicles and adjusted one of them using
sound design such that the sporty qualities of the engine were
clearly audible. Subsequent test drives showed that test persons,
despite measurably identical longitudinal dynamics, judged the
driving performance of the vehicle with integrated Active Sound
Design to be better. The subjective in-vehicle impression was
comparable to the sensation of an accelerating car with a stronger
engine. This means more fun while driving withidentical driving behaviour and equivalent fuel consumption.

Sound design for diesel vehicles — never before attained
sporty sound.The augmented dynamic experience should now benefit drivers of
diesel vehicles as well. While diesel engines are highly efficient,
in acoustic terms they aren't considered the epitome of dynamics and
driving pleasure. And that is although a modern diesel engine has
very sporty performance characteristics and is measurably superior
to comparable petrol engines thanks to its high torque at starting
and acceleration.

Diesel engines' harsher firing pulses during combustion, which
are inherent to their functionality, are responsible for the
characteristic sound. This undesirable acoustic characteristic of
diesel engines has been brought to a very low level through
intelligent acoustic lightweight construction. This makes room for
Active Sound Design, which supports a sporty sound quality. In this
way even objective aspects of driving performance are able to be
heard.

"Today's diesel engines are capable of a lot. They're
efficient, highly effective and high-torque, but until now they were
lacking the right sound. With Active Sound Design, they're finally
achieving the sound that they deserve based on their performance characteristics."

Good sound is hard work.In order to produce a special audio experience and allow a
diesel engine to sound as sporty as it feels, the sound designers
optimally adapt the sound to the vehicle and its engine performance
with great attention to detail. Too much sound with too little
engine performance is just as undesirable as minimal time delays,
because the human ear is very precise. The engine sound must
constantly provide for a harmonious driving experience. The
particular challenge here is allocating the right dosage of sound in
all driving situations and creating an authentic character.

Active Sound Design allows for significantly more systematic and
finer adjustments than classic sound design, which is oriented
around the intake and exhaust systems. "Even minimal changes to
vehicle sound can have a big impact, since human hearing
subconsciously evaluates acoustic surroundings like a
high-performance analyser and all changes are continuously
registered in the brain." Through their know-how and
experience, the BMW Group's sound experts know exactly what sound
properties must be changed to attain the desired result. At the BMW
Group, specialists from Sound Design and Psychoacoustics cooperate
closely with the engineers from Engine Development. With a clear
idea of a sporty diesel sound, they've created an entirely new and
impressive audio character for a sport coupé with a diesel engine.

The result is convincing.The sound-optimised test vehicle, based on the BMW 635d, has its
own very dynamic audio character. The noise typical for diesel
vehicles is eliminated and instead, the driver hears a very sporty,
superior sound. The entire rpm range is accompanied by harmonious,
varied and ever-appealing acoustics that make the high torque
audible at lower rpms and also provide for fun at high rpms. Active
Sound Design emphasises the existing driving dynamics of the engine
and makes them immediately audible and tangible.

"The actively designed diesel sound is hard to put into
words — it's unmatched. It has a strong character that sounds
pleasant and provides for driving dynamics and pleasure across the
entire rpm range.

(Dr. Alfred Zeitler, Acoustic Psychologist)

A team of physicists, engineers, sound designers and
psychologists are working on Active Sound Design. Although they
employ electronic tools and machines from analysis to simulation and
test drives, end the human ear is the ultimate measure.

Dynamics and efficiency through acoustics.Through the combination of measures for acoustic lightweight
construction with Active Sound Design, the customer experiences a
completely new vehicle sound and can enjoy the benefits of a modern
diesel engine'sdynamics and efficiency even
more. The noise level remains low at constant driving speed, such as
during a long trip. The driver only hears gentle rolling and wind
noises. In dynamic driving segments, like acceleration, the engine
emerges from the background and demonstrates its performance to the
driver. The driver experiences driving dynamics with all senses,
along with increased driving pleasure.

CO2 emission information.

Fuel consumption figures based on the EU test cycle, may vary depending on the tyre format specified. Further information on official fuel consumption figures, specific CO2 emission values and the electric power consumption of new passenger cars is included in the guideline “Guideline for fuel consumption, CO2 emissions and electric power consumption of new passenger cars", which can be obtained from all dealerships, from Deutsche Automobil Treuhand GmbH (DAT), Hellmuth-Hirth-Str. 1, 73760 Ostfildern-Scharnhausen and at http://www.dat.de/en/offers/publications/guideline-for-fuel-consumption.html.

Related Video Content.

Fuel consumption figures based on the EU test cycle, may vary depending on the tyre format specified. Further information on official fuel consumption figures, specific CO2 emission values and the electric power consumption of new passenger cars is included in the guideline “Guideline for fuel consumption, CO2 emissions and electric power consumption of new passenger cars", which can be obtained from all dealerships, from Deutsche Automobil Treuhand GmbH (DAT), Hellmuth-Hirth-Str. 1, 73760 Ostfildern-Scharnhausen and at http://www.dat.de/en/offers/publications/guideline-for-fuel-consumption.html.